As a rule, reservoirs for cosmetics of the kind described above have a rectangular or oval, but in any way not circular symmetrical cross-section, so that achieving an attractive appearance, in the closed state substantially depends on insuring that the external walls of the screw cap and the reservoir are in exact alignment or are oriented one in relation to the other in a defined manner. In principle, the same is true for reservoirs or screw caps of circular cross section with a label continuously extending over both, the reservoir and the cap, which equally requires an exact positioning of the screw cap. This is achieved in that at least one stop shoulder is provided limiting the end position in a defined manner, and a return stop is provided, which as a rule consists of a locking projection and a locking recess, and which prevents the screw cap from returning from its position where it rests against the stop shoulder. Various embodiments of such an arrangement are known, such as German utility model 87 12 015.
With reservoirs of comparatively hard plastic materials this closing technique has shown excellent results. However, problems come up with the use of reservoirs of softer plastics, for example of polypropylene, polyethylene, low-pressure polyethylene, acrylo-nitrile butadiene styrene co-polymers (ABS) or polyethylene terephthalate. The use of such plastics is necessary or desirable for example with highly aequous liquids because of the more favorable barrier properties of these softer plastic materials. In the case of such comparatively soft plastic materials the return stop as well as the stop shoulder are found to be subject to a comparatively high wear, in that the comparatively soft plastic material is worn off and deformed after a few closings, so that the desired defined closing position is no longer realized.